fix: Remove video tags during AI conversation voice playback

Author: shaohuzhang1

ui/src/components/ai-chat/component/operation-button/ChatOperationButton.vue

@@ -219,6 +219,8 @@ function markdownToPlainText(md: string) {
       .replace(/`(.*?)`/g, '$1')
       // 移除代码块 ```code```
       .replace(/```[\s\S]*?```/g, '')
+      // 移除video标签
+      .replace(/<video>[\s\S]*?<\/video>/g, '')
       // 移除html标签
       .replace(/<[^>]+>/g, '')
       // 移除多余的换行符